This application is based on Japanese Patent Application No. 11-241790 filed Aug. 27, 1999, the content of which is incorporated hereinto by reference.
1. Field of the Invention
The present invention relates in general to a control apparatus for an automatic transmission of an automotive vehicle, and more particularly to an upshift of the automatic transmission while the vehicle is running in a power-off state.
2. Discussion of the Related Art
There is widely known a power transmitting system for an automotive vehicle, which includes (a) an automatic transmission which is shifted up from a presently established lower-gear position to a higher-gear position having a lower speed ratio than the presently established lower-gear position, by an engaging action of a frictional coupling device by the corresponding hydraulic cylinder, and (b) a hydraulic control device for supplying a pressurized fluid to the hydraulic cylinder to effect the engaging action of the frictional coupling device. JP-A-9-295526 discloses an example of such a power transmitting system including a control apparatus adapted to limit the output of an engine of the vehicle until an upshift of the automatic transmission is completed, where an accelerator pedal is operated in the process of that upshift which was initiated during running of the vehicle with the accelerator pedal placed in the non-operated position. JP-A-9-170654 discloses a power transmitting system including a control apparatus having a pressure regulating device which is adapted to control the pressure of the pressurized fluid to be supplied to the above-indicated hydraulic cylinder such that the fluid pressure is changed at a suitable rate in the process of an upshift of the automatic transmission, or such that the fluid pressure is feedback-controlled so as to change the input speed of the automatic transmission at a suitable rate.
The conventional control apparatus for such power transmitting systems for a motor vehicle is not satisfactory in the control of an upshift of the automatic transmission. For example, the drivability of the vehicle is deteriorated if the engine output is limited until the upshift is completed, where the accelerator pedal is operated in the process of the upshift. If the frictional coupling device is engaged only after the accelerator pedal is subsequently released to its non-operated position, an engine brake may be applied to the vehicle with a result of the vehicle deceleration unexpectedly to the vehicle operator. In the absence of the pressure regulating device indicated above, the moment at which the frictional coupling device has been engaged would tend to differ from the moment at which the input speed of the automatic transmission has reached the synchronizing speed of the higher-gear position. If the generation of the engaging force of the frictional coupling device is initiated before the input speed has reached the synchronizing speed, the vehicle tends to be accelerated unexpectedly to the vehicle operator. If the generation of the engaging force is initiated after the input speed has reached the synchronizing speed, the vehicle tends to be decelerated unexpectedly to the vehicle operator. The latter deceleration is remarkable particularly where the speed of the vehicle drive power source (e.g., engine speed) is raised by an engine braking effect. Even where this engine speed rise is restricted by a one-way clutch which allows the engine speed to be lowered, the vehicle may be unexpectedly decelerated due to a change in the rotating speed of the rotary members of the automatic transmission.
It is accordingly an object of the present invention to provide a control apparatus for an automatic transmission of an automotive vehicle, which permits an improved control of an upshift of the automatic transmission during running of the vehicle with the accelerator pedal placed in the non-operated position, more particularly, a control apparatus which, in the absence of the above-indicated pressure regulating device, permits adequate engagement of the frictional coupling device in a suitably timed relationship with the moment at which the input speed of the automatic transmission has reached the synchronizing speed, and more specifically, a control apparatus which permits adequate engagement of the frictional coupling device, so as to prevent deterioration of its durability and minimize unexpected deterioration of the vehicle drivability, when the accelerator pedal is operated in the process of the upshift, and which is effective to prevent unexpected deceleration of the vehicle due to an engine braking effect when the accelerator pedal is subsequently released.
The above object may be achieved according to a first aspect of the present invention, which provides an apparatus for controlling a power transmitting system of an automotive vehicle, the power transmitting system including (a) an automatic transmission which is shifted up from a presently established lower-gear position to a higher-gear position having a lower speed ratio than the lower-gear position, by an engaging action of a frictional coupling device which is operated by a hydraulic cylinder, and (b) a hydraulic control device for supplying a pressurized fluid to the hydraulic cylinder to effect the engaging action of the frictional coupling device, the apparatus comprising: (a) synchronizing time estimating means for estimating a synchronizing time required for an input speed of the automatic transmission to reach a synchronizing speed of the higher-gear position, in the process of an upshift of the automatic transmission during running of the vehicle in a power-off state in which a vehicle drive force is not transmitted to drive wheels of the vehicle through the automatic transmission; (b) a time data memory storing a predetermined stroking time required for a piston of the hydraulic cylinder to reach an engaging stroke end; and (c) timing determining means operable in response to a command to effect said upshift during running of the vehicle in said power-off state, for comparing the synchronizing time with the predetermined stroking time, and thereby determining a point of time at which a supply of the pressurized fluid to the hydraulic cylinder is initiated.
The term xe2x80x9cpower-off statexe2x80x9d of the vehicle is interpreted to mean a state in which the vehicle drive force is not transmitted from a vehicle drive power source such as an engine to the vehicle drive wheels through the automatic transmission. This xe2x80x9cpower-off statexe2x80x9d includes not only a state in which the operator""s required output of the drive power source is zero, namely, a state in which the accelerator pedal or other accelerating member for accelerating the vehicle is in the non-operated position, but also a state in which the vehicle drive force is not transmitted to the drive wheels because the operating amount of the accelerating member is smaller with respect to the running speed of the vehicle.
In the vehicle transmission control apparatus according to the first aspect of the present invention constructed as described above, the synchronizing time estimating means estimates the synchronizing time required for the input speed of the automatic transmission to reach the synchronizing speed of the higher-gear position to which the automatic transmission is shifted up, and the timing determining means compares the estimated synchronizing time with the predetermined stroking time stored in the time data memory, and thereby determines the point of time at which the supply of the pressurized fluid to the hydraulic cylinder is initiated. This control arrangement permits the frictional coupling device to be engaged in a suitably timed relationship with the point of time at which the input speed of the automatic transmission has substantially reached the synchronizing speed, irrespective of a variation in the rate of change of the input speed due to a variation in the operating characteristics of the engine. Thus, the present control apparatus is effective to minimize: an unexpected acceleration of the vehicle in the process of the upshift of the automatic transmission in the power-off state of the vehicle, which unexpected acceleration would occur if the generation of the engaging force of the frictional coupling device is initiated before the input speed has reached the synchronizing speed; and an expected deceleration of the vehicle which would occur if the generation of the engaging force is initiated after the input speed has reached the synchronizing speed.
The automatic transmission to which the control apparatus of the present invention is applicable may include a plurality of planetary gear sets, and a plurality of hydraulically operated frictional coupling devices such as clutches and brakes for connecting rotary elements of the planetary gear sets to each other or fixing those rotary elements to the housing of the automatic transmission. In this case, a selected on of a plurality of operating positions of the automatic transmission which have respective different speed ratios is established by engaging and releasing actions of the appropriate frictional coupling devices. The automatic transmission may be automatically shifted up in response to a shifting command which is generated on the basis of the vehicle running speed and the operating amount of the accelerator pedal or accelerating member. Alternatively, the automatic transmission is commanded to effect an upshift in response to an operation of a shift lever or switch by the vehicle operator. The automatic transmission equipped with the present transmission control apparatus may use a drive power source selected from among various drive power sources presently available, such as an engine operated by combustion of a fuel, and an electric motor operated with an electric energy.
The timing determining means operable in the power-off state may be operated only when the upshift of the automatic transmission is effected while the accelerating member is in the non-operated position. However, the timing determining means may be operated when the upshift is effected while the accelerating member is in an operated position, as long as the power-off state (in which a vehicle drive force is not transmitted from the vehicle drive power source to the vehicle drive wheels through the automatic transmission) is detected, for example, on the basis of the rotating speeds of the input and output members of a torque converter connected to the automatic transmission. The upshift may be a so-called xe2x80x9cclutch-to-clutch shifting actionxe2x80x9d of the automatic transmission in which the frictional coupling device indicated above is engaged to establish the higher-gear position while at the same time another frictional coupling device which has been engaged to establish the lower-gear position is released. Alternatively, the upshift may be effected by controlling the engaging action of only the frictional coupling device which is engaged to establish the higher-gear position. In this case, the automatic transmission uses a one-way clutch to establish the higher-gear position, without the clutch-to-clutch shifting action.
In one preferred form of the first aspect of this invention, the synchronizing time estimating means detects a rate of change of the input speed, obtains the synchronizing speed on the basis of a speed ratio of the higher-gear position and an output speed of the automatic transmission, and calculates the synchronizing time by dividing a difference between the obtained synchronizing speed and the input speed by the rate of change of the input speed.
The output speed of the automatic transmission, which represents the vehicle running speed, may be considered substantially constant. However, the synchronizing speed may be estimated with higher accuracy, if the output speed and a rate of change of the output speed are used in addition to the input speed and the rate of change of the input speed.
The stroking time required for the piston of the hydraulic cylinder to reach the engaging stroke end differs depending upon the hydraulic pressure in the hydraulic control device. Usually, this hydraulic pressure is adjusted according to the output of the vehicle drive power source, for instance, the opening angle of the throttle valve of the engine. In this respect, it is preferred that the stroking time be determined or adjusted depending upon the output of the vehicle drive power source (e.g., opening angle of the throttle valve). The stroking time may be determined on the basis of other parameters such as the temperature of the working fluid, which influences the stroking time. To eliminate a difference in the characteristic between the individual hydraulic cylinders used in different vehicles to effect the upshift in question, the stroking time may be determined by actually detecting the time required for the piston to reach the engaging stroke end. In this case, the stroking time stored in the time data memory is updated by learning compensation based on the detected time.
The timing determining means is basically arranged to initiate the supply of the pressurized fluid to the hydraulic cylinder of the frictional coupling device, when the synchronizing time has become substantially equal to the stroking time. To prevent a shifting shock in the process of the upshift in the power-off state, the point of time at which the supply is initiated may be purposely delayed so that the generation of the engaging force of the frictional coupling device is initiated only after the input speed has reached the synchronizing speed. Further, to prevent an unexpected deceleration of the vehicle in the process of the upshift, the point of time at which the supply is initiated may be purposely advanced so that the generation of the engaging force is initiated before the input speed has reached the synchronizing speed.
The object indicated above may also be achieved according to a second aspect of this invention, which provides an apparatus for controlling a power transmitting system of an automotive vehicle, the power transmitting system including (a) an automatic transmission which is shifted up from a presently established lower-gear position to a higher-gear position having a lower speed ratio than the lower-gear position, by an engaging action of a frictional coupling device which is operated by a hydraulic cylinder, and (b) a hydraulic control device for supplying a pressurized fluid to the hydraulic cylinder to effect the engaging action of the frictional coupling device, the apparatus comprising: input torque limiting means operable in response to an increase in an amount of operation of an accelerating member for accelerating the vehicle, in the process of an upshift of the automatic transmission during running of the vehicle in a power-off state in which a vehicle drive force is not transmitted to drive wheels of the vehicle through the automatic transmission, the input torque limiting means limiting an input torque of the automatic transmission for a predetermined torque limiting time necessary to permit the frictional coupling device to have a torque capacity sufficient to prevent deterioration of its durability; and hydraulic pressure compensating means operable when the input torque is limited by the input torque limiting means, for increasing a line pressure of the hydraulic control device to increase a rate at which the pressurized fluid is supplied to the hydraulic cylinder.
The vehicle transmission control apparatus according to the second aspect of the invention is constructed to prevent deterioration of the durability of the friction members of the frictional coupling device, owing to an operation of the input torque limiting means to limit the input torque of the automatic transmission for a predetermined torque limiting time necessary for the frictional coupling device to have the torque capacity sufficient to prevent deterioration of its durability, when the accelerating member is operated, in the process of the upshift of the automatic transmission during running of the vehicle in the power-off state. The present apparatus is effective to minimize a shortage in the vehicle drive force upon operation of the accelerating member, while preventing the deterioration of durability of the friction members of the frictional coupling device with a minimum torque limiting time. Further, the line pressure of the hydraulic control device is temporarily raised during the input torque limiting control so that the pressurized fluid can be rapidly supplied to the hydraulic cylinder, to permit the frictional coupling device to be rapidly engaged to have the suitable torque capacity. Accordingly, the input torque limiting time can be further shortened, and the shortage of the vehicle drive force is effectively ameliorated.
The input torque limiting means and the hydraulic pressure compensating means operable in the power-off state may be operated only when the upshift of the automatic transmission is effected while the accelerating member is in the non-operated position. However, the input torque limiting means and the hydraulic pressure compensating means may be operated when the upshift is effected while the accelerating member is in an operated position, as long as the power-off state is detected, for example, on the basis of the rotating speeds of the input and output members of a torque converter connected to the automatic transmission. The upshift may be a so-called xe2x80x9cclutch-to-clutch shifting actionxe2x80x9d of the automatic transmission in which the frictional coupling device indicated above is engaged to establish the higher-gear position while at the same time another frictional coupling device which has been engaged to establish the lower-gear position is released. Alternatively, the upshift may be effected by controlling the engaging action of only the frictional coupling device which is engaged to establish the higher-gear position. In this case, the automatic transmission uses a one-way clutch to establish the higher-gear position, without the clutch-to-clutch shifting action.
In one preferred form of the second aspect of the invention, the torque limiting time during which the input torque is limited by the input torque limiting means even after the increase in the amount of operation of the accelerating member is determined on the basis of a time lapse after a point of time at which the supply of the pressurized fluid to the hydraulic cylinder by the pressure control device is initiated to effect the upshift.
In one advantageous arrangement of the above preferred form, the torque limiting time is determined according to a predetermined relationship between the torque limiting time and the time lapse between the point of time at which the supply is initiated and a point of time at which the amount of operation of the accelerating member is increased, such that the torque limiting time decreases with an increase in the time lapse.
The torque capacity of the frictional coupling device which does not deteriorate the durability of the frictional coupling device does not necessarily mean full or complete engagement of the frictional coupling device. The torque limiting time may be a length of time necessary for the piston of the hydraulic cylinder to reach the engaging stroke end to initiate the generation of the engaging force or torque by the frictional coupling device. Further, the input torque of the automatic transmission may be limited until the detected or estimated pressure in the hydraulic cylinder has been raised to a predetermined level which permits the frictional coupling device to have a torque capacity sufficiently large to prevent deterioration of its durability.
Where the output of the vehicle drive power source is electrically controlled according to a change in the operating amount of the accelerating member, the input torque limiting means may be adapted to prevent or limit an increase of the output of the vehicle drive power source. Where the vehicle drive power source is mechanically connected directly to the accelerating member, the input torque limiting means may be adapted to release or partially engage an input clutch between the automatic transmission and the drive power source, in order to limit the input torque of the automatic transmission. Where the vehicle drive power source is an engine, the input torque of the automatic transmission may be limited by controlling the ignition timing of the engine or the amount of fuel injection into the engine.
Where the hydraulic control device is arranged such that the line pressure is increased with an increase in the output of the vehicle drive power source (increase in the opening angle of a throttle valve), the line pressure would not be raised when the output of the drive power source is not increased with an increase in the amount of operation of the accelerating member. In the presence of the hydraulic pressure compensating means according to the second aspect of this invention, the line pressure can be temporarily increased according to an increase in the amount of operation of the accelerating member. For instance, the line pressure is temporarily raised to a level determined on the basis of a compensated operating amount of the accelerating member, which is obtained by multiplying the actual operating amount of the accelerating member with a suitable compensating coefficient (larger than 1).
The object indicated above may also be achieved according to a third aspect of the present invention, which provides an apparatus for controlling a power transmitting system of an automotive vehicle, the power transmitting system including (a) an automatic transmission which is shifted up from a presently established lower-gear position to a higher-gear position having a lower speed ratio than the lower-gear position, by an engaging action of a frictional coupling device which is operated by a hydraulic cylinder, and (b) a hydraulic control device including a pressure regulating device for supplying a pressurized fluid to the hydraulic cylinder to effect the engaging action of the frictional coupling device, and for controlling a pressure of the pressurized fluid to be supplied to the hydraulic cylinder, the apparatus comprising engaging and releasing control means operable in the process of an upshift of the automatic transmission, for controlling the pressure regulating device such that the pressurized fluid is supplied to the hydraulic cylinder to effect the engaging action of the frictional coupling device while an accelerating member for accelerating the vehicle is in operation, and such that a piston of the hydraulic cylinder is held at a standby position close to an engaging stroke end thereof, while the accelerating member is not in operation, the frictional coupling device being placed in a released state thereof when the piston is held at the standby position.
The accelerating member, which may be an accelerator pedal, is operated by the vehicle operator when the vehicle operator wants to accelerate the vehicle, and is held in its non-operated position when the vehicle operator does not want to accelerate the vehicle.
In the vehicle transmission control apparatus constructed according to the third aspect of the invention described above, the pressure regulating device is controlled to supply the pressurized fluid to the hydraulic cylinder to effect the engaging action of the frictional coupling device while the accelerating member is placed in an operated position, and hold the piston of the hydraulic cylinder at its standby position close to the engaging stroke end, for holding the frictional coupling device in its released state, while the accelerating member is placed in its non-operated position. This arrangement prevents the application of an engine brake to the vehicle and consequent unexpected deceleration of the vehicle, even in the absence of a one-way clutch to effect the upshift. Further, the piston of the hydraulic cylinder is held at the standby position close to the engaging stroke end, the frictional coupling device can be engaged to establish the higher-gear position in a relatively short time after a subsequent operation of the accelerating member, so that the vehicle drive force can be produced shortly after the accelerating member is operated. Thus, the engaging and releasing control means provided according to this third aspect of the invention provides substantially the same effect as achieved by the one-way clutch.